This invention relates generally to window covering hardware and, more specifically, to a roller shade system for raising and lowering a roller shade.
A number of different systems for raising and lowering shades are in use today in the window covering industry. Typically, the systems include a roller coupled to a clutch controlled with a cord or chain. Opposite to the clutch is an idler. The idler and clutch are typically suspended on brackets mounted to a window frame. A clutch bracket typically engages a feature on the clutch strong enough to hang a shade. An idler bracket typically rotatably engages the idler, allowing the idler to rotate with the shade while holding the idler and the shade in place.
Typically the clutch consists of a cylindrical shaft, pulley and a housing as well as a torsion spring. The torsion spring provides a force necessary to hold the weight of the shade in place. The spring is placed on the shaft and the pulley is placed over the spring and the shaft. Both ends of the spring are bent and the pulley engages the bent ends of the spring. Rotation of the pulley expands the spring allowing the spring to slip over the shaft. The housing is placed over the pulley and has keys engaging the spring in opposite directions. Rotation of the housing contracts the spring preventing the spring from rotating.
In prior art clutch designs, the load on the spring was either concentrated on one side, or was distributed symmetrically between pairs of springs located on opposite sides of the shaft. Both designs have shortcomings. In a system using a clutch with one spring, a load on the bent spring ends changes the position of the bent portions relative to the shaft. The load is smallest when the spring is rotating down and largest when rotating up. This uneven load distribution during rotation causes uneven friction and uneven effort to operate the shade. In a system using a clutch with symmetrical spring orientation, much higher forces are required to rotate the springs if the bent portions of the opposing springs are in a vertical plane. Additionally, the use of an even number of springs creates a cancelling moment that requires added force to overcome. Thus, a force required to raise and lower the shade varies depending upon the position of the springs and corresponding tangs. Such variations inhibit smooth raising and lowering of the shade.
Prior roller shade systems suffered from other defects, such as wobbly or hard to connect clutch and idler brackets. Moreover, prior roller shade systems are difficult to mount level and if mounted even slightly out of level may lead to obviously misaligned shades when the shades are lowered.
Accordingly, there is a need for an improved roller shade system that remedies the shortcomings of the prior art.